Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole with a small surface area at an air bearing surface (ABS) and a flux return pole (opposing pole) which is magnetically coupled to the main pole and has a large surface area at the ABS. Critical dimensions of the main pole include a neck height and a pole width in a pole tip adjacent to the ABS. Magnetic flux generated in the main pole layer passes through the pole tip into a magnetic media and then back to the write head by entering the flux return pole.
A PMR magnetic recording head combined with a double layered media has enabled numerous advancements in the technology and a continuous increase in hard disk drive (HDD) recording density beyond 100 Gb/in2. However, as track width shrinks, the write field decreases due to a small pole tip area and pole tip saturation if head-media spacing reduction cannot be applied suitably. As a result, this situation imposes a difficult challenge to achieve 1 Tb/in2. Thus, the lack of a strong write field limits current narrow track recording and presents an earlier obstacle for areal density growth than reaching the media super paramagnetic limit.
Fortunately, new technology options are being explored that promise to provide areal density growth beyond the aforementioned limits. New developments such as bit patterned magnetic recording (BPMR) and heat assisted magnetic recording (HAMR) are attractive but come with considerable risk and significant challenges in terms of manufacturing process, cost, and reliability. On the other hand, another candidate known as microwave assisted magnetic recording (MAMR) is expected to be easier and more practical to implement because the additional component is only a spin torque oscillator (STO) in PMR heads with conventional PMR media. The STO manufacturing process is essentially the same as for current tunnel magnetoresistive (TMR) heads, but is fabricated in the trailing gap between the main pole and trailing shield. Therefore, the main pole and STO must be integrated with the same or similar track width.
Referring to FIG. 1 part (a), a wide main pole 2 is shown with a narrow STO 1a having a width w that is substantially less than the width of the trailing edge 2t of the main pole along the cross track (x-axis) direction. Note that the main pole 2 and STO 1a move in a down track (z-axis) direction over a magnetic media to produce wide written tracks 3 having a width that essentially corresponds to the width of the trailing edge 2t. Since the field generation layer (FGL) of the STO is very thin and field amplitude is limited, the switching field reduction of the media is also limited. In conventional designs, the main pole has to be able to write without any assist but in MAMR designs, the assist by the STO brings further improvement to writing performance. Consequently, it is an advantage for both of the main pole and STO to have a narrow track design. For example, in FIG. 1 part (b), STO 1b has a width w1 essentially equal to that of the trailing edge of main pole 4. In part (c), STO 1c has a width w2 slightly less than main pole 4, and in part (d), STO 1d has a width w3 slightly larger than the trailing edge of main pole 4. As a result, each of the main pole/STO configurations represented in FIG. 1 parts (b)-(d) are able to write narrow tracks 5.
A search of the prior art was performed to identify main pole structures having a narrow pole tip made by ion milling. In U.S. Pat. No. 7,394,621, a method is disclosed for trimming a pole tip by ion milling. The main pole which is not tapered at the ABS is trimmed and then a top yoke is fabricated on the main pole to define a neck height for the pole tip portion.
U.S. Pat. No. 7,337,530 teaches a trimmed and side beveled pole tip where a shield layer is used as a mask to trim the write pole. The S3 shield is trimmed concurrently with the write pole to simplify the manufacturing process and has essentially the same width as the track width of the write pole.
In U.S. Patent Application 2006/0044677, the trailing edge of a pole tip is on a trimmed rectangular shaped portion of the write pole while the leading edge is on a trapezoidal shaped portion of the write pole.
U.S. Patent Application 2006/0002024 describes a write pole with a leading edge taper.
Unfortunately, there is no prior art method available that can be relied upon to fabricate a narrow main pole having a track width approaching 50 nm and an overlying STO having a similar width for MAMR applications. Furthermore, a narrow main pole/STO design is needed that enables a large field at the ABS while minimizing side track erasure.